Okiez...this seems long time ago, but seems you guys have lots of questions, I'll just type what I know.
I remember it was like 10 out of 125 or something like that getting the scholarship.
I know a person getting it with UAI as low as 98.65(but with damn lots of extra-curriculars) and people with UAI of 99.65 missing out,so I don't think it's entirely based on UAI. However, UAI99.9+ definitely gets you one because that is rare in this uni.(The highest UAI was 99.85 or something like that in the uni in my year).
And yes we do usuaully have about one hundred students getting UAI above 98.5 before merit scholarship was introduced. There was something called innovation scholarship before my year where everyone gets $4000 if their UAI is above 98.5. However, from my year and onwards they replaced this with this thing. which gets them to apply for this and because not many students are getting it, they switched to UNSW or USYD off in later rounds, which is why we only have 44 students getting UAI above 98.5 this year (will be 43 provided that I wasn't stupid enough.) Now this is reminding me of sh**ty past because I have more reason than most of these 80 students on changing their preference in the late round. I actually got an offer of Academic Achievement Award scholarship from UNSW for being a dux in my school. But I was stupid enough to have too much faith in my ex-girlfriend otherwise it's very likely that I change the prefererence in the later rounds and the dream turned out to be disastrous shortly after late round deadline passed.
The merit scholar program is automatic (it's not a scholarship,it's a program that everyone gets in) and almost useless except you get to meet the Vice-Chancellor lots times for his event (you get invitations, but it's boring so I just don't go to most of them). And you get assigned with a mentor where you can get lots of info's(especially with the pass rate issue). Other than that, since they do not have a solid plan on this, most of the things stated in the AD do not exist.